RNA interference (RNAi) is a mechanism capable of inhibiting the expression of a gene in a highly specific and efficient manner, in which degradation of the mRNA of a target gene is induced by introducing a double-stranded RNA, which comprises a sense strand having a sequence homologous to the mRNA of the target gene and an antisense strand having a sequence complementary to the mRNA of the target gene, into cells or the like, thereby inhibiting the expression of the target gene.
In most siRNAs which have been used in the art, the length of the antisense strand is limited to 19-23 nucleotides (nt). This is because the structure of siRNAs which have been used by researchers mimics the structure of products obtained by cutting long dsRNAs in cells by a dicer (Elbashir et al. Nature 2001, 411:494-498). In addition, early X-ray crystallography studies suggested a model in which the 5′ and 3′ ends of the siRNA antisense strand introduced into Argonaute-2 (Ago2) that is the key element of a RISC complex are bound to the mid domain and the binding pocket of the PAZ domain, respectively (Song et al. Nat. Struct. Biol. 2003, 10: 1026-1032), but subsequent studies revealed that the 3′ end following the 16th nucleotide of the antisense strand is not bound to the PAZ domain (Wang et al. Nature 2009, 461: 754-761). This suggests that there can be flexibility in the sequence and length of the 3′ end of the siRNA antisense strand.
Meanwhile, an additional study on siRNA reported a modified siRNA-DNA construct, which comprises a single-stranded DNA molecule that can function as a primer for PCR to detect siRNA in a sample (US 2009/0012022 A1). However, the modified siRNA-DNA construct merely has an additional tool for quantification, but has no positive influence on the efficiency with which a target gene is inhibited.
Accordingly, the present inventors have made extensive efforts to a novel, RNAi-inducing nucleic acid molecule which inhibits a target gene with increased efficiency, and as a result, have designed a double-stranded nucleic acid molecule comprising a first strand, which is 24-121 nt in length and comprises a region complementary to a target nucleic acid, and a second strand which is 13-21 nt in length and has a region that binds complementarily to the region of the first strand, which is complementary to the target nucleic acid, and the present inventors have predicted that a nucleic acid oligonucleotide contained in the single-stranded region at the 3′ end of the first strand will target other target genes or guide this nucleic acid molecule to the target gene. In addition, the present inventors have constructed a nucleic acid molecule structure, which has a long single-stranded region at the 3′ end of the first strand, using an siRNA structure (Korean Patent Laid-Open Publication No. 10-2009-0065880 filled by the present inventors) which shows minimized off-target effects and does not saturate the RNAi machinery, and the present inventors have predicted that a nucleic acid oligonucleotide, which is contained in the single-stranded region at the 3′ end of the first strand, can show the effect of targeting other target genes or guiding the siRNA at the 5′ end to the target gene, while off-targeting effects will be minimized, thereby completing the present invention.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present invention, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.